Electrochemical cells utilizing solid ionic conductors have many potential advantages. For example, alkali metals, such as sodium and lithium, are attractive for use as negative electrodes because of their electromotive potential. However, these metals react vigorously with water and therefore cannot be used in conventional cells. Use of a solid ionic conductor offers the possibility of employing alkali metal electrodes. Another example of the possible advantages afforded by solid ionic conductors involves electrode fabrication. Many materials utilized as reactants in an electrode are insulators and must be mixed with an electron conductor to form a composite electrode. Such electrodes, when functioning in a cell, produce two interfaces, a reactant-electron conductor interface and an electron conductor-electrolyte interface. The use of an ionic conductor, which also exhibits electronic conductivity, eliminates one interface.
Investigation for suitable ionic conductors has been intense. (A survey of ionic conductivity and a compilation of known ionic conductors can be found in Holzapfel and Rickert, "High Ionic Conductivity in Solids--Theoretical Aspects and Applications", Advances in Solid State Physics, XV (Pergamon-Viking 1975), compilation at page 322.) Recently, an investigation on the ionic conductivity of some II-VI compounds has been reported. (See R. Galli and F. Garbassi, Nature, 253, 702 (1975).) Because of their potential advantages, the search for new, solid ionic conductors is presently being actively pursued.